Bipartisan talks aimed at resolving the border wall dispute and averting a government shutdown on Friday have broken down and are at an impasse, lawmakers and others familiar with the situation said on Sunday.

The sticking point is over detention beds, both people said, an issue that would typically be regarded as a side-note to the broader talks on the level of funding for border security.

Mick Mulvaney, the acting White House chief of staff, said Sunday that a shutdown isn't the most likely option but that he “absolutely cannot” rule it out.

Talks could still get back on track, but the prospect of a longer-lasting deal breaking down seem to have increased. Without a funding deal, nine federal departments and related agencies would shutdown again after Friday. Negotiators had hoped to unveil a deal Monday to set up votes in the House and Senate before the shutdown deadline.

Senator Jon Tester, Democrat of Montana, said on the same broadcast that he was “not positive we'll get to a deal.”

Mulvaney spoke as Congressional negotiators continue talks on a security plan that includes some sort of barrier on the border, hoping to complete a deal to avert another government shutdown. It wasn't fair to say that Trump would sign whatever Congress comes up with, Mulvaney said, terming the level of proposed border wall funding “all over the map.”

“He's going to do whatever he legally can to secure the border,” Mulvaney said of President Donald Trump on NBC's “Meet the Press,” one of two scheduled appearances on Sunday talk shows.

“You cannot take a shutdown off the table, and you cannot take $5.7 (billion) off the table,” he said, referring to the level of funds Trump has been demanding for a wall on the U.S.-Mexican border.

As of Saturday it seemed that negotiators were homing in on a proposal with border barrier funding of between $1.3 billion and $2 billion, said a person familiar with the talks. Democrats are making a higher level of funding for barriers contingent on the new cap for beds, something Republicans are resisting.

Trump was back in the fray late Saturday afternoon, indicating in a tweet that if Democrats didn't give him all the wall money he's demanded, he may use executive action to build it. Democrats have warned such action would face court challenges, and some Republicans have suggested it's an option best avoided.

Democrats also want a provision saying the U.S. Customs and Border Protection agency, which like ICE is part of the Department of Homeland Security, must prioritize capturing violent criminals in using that cap. Republicans have said violent criminals caught inside the U.S. shouldn't count toward the cap.